Various prosthetic systems have been designed employing myoelectrically controlled and similarly controlled power units. Included in such systems are those which provide powered elbow action, nameley, elevation of a forearm portion provided with a hook assembly for grasping and lifting a load. With existing devices of this type there is only a minimal live-lift capacity, that is, there is a lack of ability to grasp an object weighing one-half pound or more and lift it throughout the total elbow excursion range without opening the terminal device and releasing the object. This is also true of conventional body-powered prosthesis units currently in use.
Thus, there is a substantial need for an attachment or built-in device employed with a prosthetic unit to provide the ability to operate the prosthetic elbow without opening the associated terminal device or hook for grasped objects of substantial weight, for example, objects weighing up to three pounds or more.
More specifically, there is a substantial need for a reliable means for automatically locking the terminal device or hook in a closed grasping condition during the total excursion range of the powered lifting stage of the associated forearm member, and for afterwards releasing the terminal device for normal operation.